This invention relates to an adaptive antenna device for use in a mobile communication system and, in particular, to a control method of an adaptive antenna device used in a cellular system which adopts a CDMA (code division multiple access) method.
As well known in the art, radio communication is carried out by using, as a medium, radio waves that propagate a free space. This inevitably brings about interference between a desired radio wave to be received by a desired terminal and the other radio waves to be received by the other terminals except the desired terminal. Consequently, a fundamental problem takes place such that quality of communication is indispensably reduced in both the desired radio wave and the other radio waves.
In order to solve the above-mentioned problem and to effectively utilize a radio frequency resource, consideration is made about a multiple access communication method which can not only avoid the interference but also can carry out communication among a plurality of terminals. Such a multiple access communication method may be, for example, a frequency division multiple access (FDMA) method, a time division multiple access (TDMA) method, and a code division multiple access (CDMA) method.
In either one of the multiple access communication methods, communication can be ideally carried out among a plurality of terminals without interference. However, propagation environments are actually drastically changed with time and frequency utilization efficiency should be technically improved in the practical communication in a technical viewpoint. Such a change of propagation environments and a technical requirement of improving the frequency utilization efficiency give rise to incompleteness of practical communication conditions and consequently brings about any interference.
Among the above-mentioned multiple access communication methods, the CDMA method assigns, to each communication terminal, a peculiar orthogonal code (or pseudo-noise) which has self-correlation and low cross correlation and which can be discriminated. With the CDMA method, all of the communication terminals can use the same frequency in common by distinguishing each code from one to another.
Herein, consideration is made about a mobile communication system which has movable communication terminals. In this event, each communication terminal is moved under environments or conditions that are rapidly and incessantly varied. Under the rapidly and incessantly varied conditions, the code tends to be vulnerable in orthogonality and to deteriorate quality of communication due to interference among the codes. Therefore, when the CDMA method is adopted to the mobile communication, techniques are inevitably required about transmission power control for keeping interference uniform or constant and about rake receiving and path capturing for effectively utilizing a plurality of multi-path propagation waves having different delay times.
On the other hand, recent attention has been focused on an adaptive antenna that is aimed at improving quality of communication and frequency utilization efficiency in a mobile communication system of the CDMA method.
Herein, the adaptive antenna is formed such that a plurality of antenna elements are regularly arranged to form a spatial filter and are given reception waves which have amplitudes and phases different from one another, respectively. In addition, the reception waves are controlled by giving weights such that amplitudes and phases of the reception waves become appropriate. Specifically, an antenna gain is adaptively varied with time in consideration of propagation environments so that the antenna gain becomes high in a direction of an aimed communication terminal and becomes low in a direction of an interference wave of a high level.
In the mobile communication system of the CDMA method, spatial separation is realized by adaptively controlling directivity of the adaptive antenna with this method, it is possible to reduce displacement of orthogonality in codes received by the plurality of the communication terminals which communicate through the same frequency and to therefore decrease interference between the codes. As a result, the frequency utilization efficiency can be also improved by this method.
In the meanwhile, it should be considered in the mobile communication system that the propagation environments are rapidly varied while each communication terminal is moving. In order to trace or follow such rapid variation of the propagation environments, requirements are made about capturing accurate propagation information and about very high speed performance of processing the propagation information. Recent researches enable high speed simulation. However, it is practically difficult to implement the processing performance matched with the high speed simulation. In addition, it is necessary to apply a directivity control method suitable for each propagation environment.
As a directivity control method, both a beam steering control method and a null steering control method are known in the art and will be simply often called beam steering control and null steering control below, respectively.
The beam steering control is for generating a plurality of beams partially overlapped with each other to control the beams so that a main one of the beams is directed to an aimed communication terminal. With the beam steering control, it is possible to cover a wide angle by increasing the beams in number, so as to cope with a variation of a propagation characteristic. However, the possibility that a superfluous radio wave is often picked up becomes high with an increase of the beams and the adaptive antenna becomes low in performance. Although consideration may be made about using a high speed adaptive algorithm responding to a rapid variation of a propagation characteristic, such an algorithm can not be easily implemented, as mentioned before.
On the other hand, the null steering control is for generating a wide beam which has null points directed to directions of receiving interference waves. At the null points, an antenna gain is drastically attenuated. However, an antenna gain tends to be lowered in a direction of a desired wave also in the null steering control.
In Japanese Unexamined Patent Publication No. Hei. 11-251986, namely, 251986/1999, proposal has been made about an adaptive antenna device which has a plurality of antenna elements, a first pattern forming unit for forming a first directivity pattern in a first direction, and a second pattern forming unit for forming a second directivity pattern in a second direction orthogonal to the first direction. Herein, it is to be noted that each of the first and the second forming units is operable in accordance with the same algorithm. With this structure, when either one of the first and the second directivity patterns exhibits an excellent characteristic, the remaining one of the first and the second directivity patterns exhibits an extremely bad characteristic because no correlation is present at all between the first and the second directivity patterns. The adaptive antenna device is disadvantageous in that it can not favorably follow a rapid variation of an arrival direction of the desired wave within a small angle less than 90xc2x0.
It is an object of this invention to provide an adaptive antenna device which is capable of coping with a rapid change of propagation environments without a reduction of performance.
It is another object of this invention to provide an adaptive antenna device of the type described, which can compensate defects of both beam steering control and null steering control.
It is still another object of this invention to provide a method of controlling an adaptive antenna device, which is capable of favorably following a rapid variation of an arrival direction of a desired wave. With an interference wave or a jamming wave suppressed.
It is yet another object of this invention to provide a method of the type described, which is capable of mitigating an influence of an instantaneous variation.
An adaptive antenna device to which this invention is applicable comprises a plurality of antenna arrays and a base station apparatus coupled to the antenna arrays. Each of the antenna arrays has a plurality of antenna elements spatially arranged. According to an aspect of this invention, the base station apparatus comprises combining means for forming a directivity pattern which is combined by varying an amplitude and a phase of each radio signal received by and transmitted from the antenna elements so that radio energy is increased towards a designated range and a designated direction of a communication radio wave and is cancelled in parallel towards a range and a direction of a jamming wave. The combining means comprises beam steering antenna pattern control means for forming a narrow beam to control an antenna gain so that a maximum portion of the antenna gain is directed to a received direction of the communication radio wave, null steering antenna pattern control means for carrying out a control operation such that an antenna gain has a null portion direct a received direction of the jamming wave and concurrently has a high gain portion of the antenna gain direct the received direction of the communication radio wave, and weighting means for weighting a received signal in accordance with a beam obtained by the beam steering antenna pattern control and with a beam obtained by the null steering antenna steering control.
Herein, each of the beam steering antenna pattern control means comprises arrival direction estimation means for performing each of the beam steering antenna pattern control and the null steering antenna pattern control simultaneously or in a time division fashion at a very small time interval, so as to estimate a direction of a desired wave from different amplitudes and phases of the received radio waves received from the plurality of the antenna arrays and to produce results of the estimation. The results of the estimation are defined as an angle profile which is representative of parameter information of the beam steering and the null steering antenna pattern control means.
Specifically, the beam steering antenna pattern control means comprises reception means for receiving, as control information, parameters which include a beam width in question and an angle profile for determining the direction of the beam and which selectively include a previous beam width and a previous angle profile referenced only when control operation is consecutively carried out from the past and means for attaining the antenna pattern on the basis of the control information. On the other hand, the null steering antenna pattern control means comprises receiving means for receiving, as control information, parameters which include an angle profile for determining a beam direction and a previous angle profile which is referenced only when control operation is consecutively carried out from the past and means for attaining the antenna pattern on the basis of the control information.
In addition, the base station apparatus further comprises comparing means for comparing, with each of predetermined threshold levels, each of a reception signal received through a beam patterned by the beam steering directivity control and another reception signal received through a beam patterned by the null steering directivity control, to produce a result signal representative of a result of comparison, combining means for combining the reception signal and another reception signal after each of the reception signal and another reception signal is weighted only when each signal exceeds the predetermined threshold level, and repeating means for repeating the combining operation after delay time processing is carried out to delay a predetermined time.
According to another aspect of this invention, the base station apparatus comprises a first directivity pattern generator, operable in accordance with a first algorithm, for generating a first beam which has a first directivity pattern determined by the first algorithm, a second directivity pattern generator, operable in accordance with a second algorithm different from the first algorithm, for generating a second beam which has a second directivity pattern determined by the second algorithm, and a combining unit for combining the first beam with the second beam to form a combined directivity pattern. The first algorithm and the second algorithm are used for executing beam steering control and null steering control, respectively.
In addition, the base station apparatus further comprises a third directivity pattern generator for carrying out receiving operation of a received signal in accordance with the first algorithm to produce a first processed signal, a fourth directivity pattern generator for carrying out receiving operation of the received signal in accordance with the second algorithm to produce a second processed signal, and a control unit for controlling the third and the fourth directivity pattern generators so that the first and the second processed signals become optimum in phases and amplitudes.
According to still another aspect of this invention, a method is for use in controlling an adaptive antenna device and comprises the steps of generating a first beam of a first directivity pattern in accordance with a first algorithm, generating a second beam of a second directivity pattern in accordance with a second algorithm different from the first algorithm, combining the first and the second beams to produce a combined beam of a combined directivity pattern, and controlling the combined directivity pattern in consideration of an arrival direction of a desired wave and arrival directions of jamming waves.
The first algorithm is determined for beam steering control while the second algorithm is determined for null steering control.